Soil Testing in Montana

Ask the lab for:

• Phosphorus: Olsen. Sodium bicarbonate. Made for alkaline, high-lime soils like most of the West.
• Potassium: Ammonium acetate. The long-standing potassium test. Reads close to Mehlich-3 for potassium.

Using different tests for different nutrients is normal. The soil test calculator lets you pick the test for each one.

Labs pull nutrients out of soil with different chemicals, and each one gives a different number for the same soil. 20 ppm on one test and 20 ppm on another don’t mean the same thing, so check which test your report used before you compare it to a chart.

• Basic test. pH, phosphorus and potassium, usually with calcium and magnesium. Enough for most gardens and lawns.
• Organic matter. How much organic matter the soil holds, which sets how much nitrogen it releases.
• Nitrate. Nitrate nitrogen in the soil now. Most useful in dry climates, where it carries over winter.
• Salts. Soluble salts (EC), and sodium where salt or poor drainage is a problem.
• CEC. Cation exchange capacity: how many nutrients the soil can hold on to.

• Montana's fertilizer guidelines are based on Olsen phosphorus, so ask the lab for Olsen P.
• Ask for the ammonium acetate test for potassium.
• Use a lab in a proficiency program, such as NAPT-PAP or CTS-ALP. NRCS programs require one.
• Gardens and annual crops are sampled 0 to 6 inches deep, hay and pasture 0 to 12 inches.
• Some county Extension offices mail samples to a lab for you and help read the results.

Sources: [1] [2]

• Take 10 or more small cores across the area and mix them in a clean bucket. One spot tells you about one spot.
• Sample gardens and lawns about 6 inches deep, below any mulch or thatch.
• Keep beds that are grown differently, like a lawn and a vegetable garden, as separate samples.
• Wait a couple of months after fertilizing or liming, so the test reads the soil and not the last bag.
• Use the same lab and the same tests each time, so the numbers compare from year to year.

Your county Montana Extension office can help you take the sample and read the report.

Once the report comes back, type the numbers into the soil test calculator to see what to add for your bed or lawn. The soil test guide walks through each line of the report.

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Bizon is an independent business and isn’t affiliated with or endorsed by any university or Extension service. Details were checked against each lab’s or Extension service’s own pages in October 2026. Why Bizon supports Extension.